// Package worktime computes monthly working-time roll-ups under the Korean Labor
// Standards Act model: a 주 소정근로시간 (default 40h) baseline, business-day
// expansion for the month, plus recognized leave/overtime.
package worktime

import "time"

// MonthBusinessDays returns the count of weekdays (Mon–Fri) in the given month.
// Public holidays are out of scope here; admins can adjust via leave/공가.
func MonthBusinessDays(year int, month time.Month) int {
	n := 0
	d := time.Date(year, month, 1, 0, 0, 0, 0, time.UTC)
	for d.Month() == month {
		if wd := d.Weekday(); wd != time.Saturday && wd != time.Sunday {
			n++
		}
		d = d.AddDate(0, 0, 1)
	}
	return n
}

// StandardMinutes is the expected worked minutes for the month: business days ×
// the policy's daily standard minutes.
func StandardMinutes(year int, month time.Month, dailyStandardMin int) int {
	if dailyStandardMin <= 0 {
		dailyStandardMin = 480
	}
	return MonthBusinessDays(year, month) * dailyStandardMin
}

// NetWorkMinutes computes worked minutes between clock-in and clock-out minus an
// unpaid break. Returns 0 if either bound is missing or the span is negative.
func NetWorkMinutes(in, out *time.Time, lunchMinutes int) int {
	if in == nil || out == nil {
		return 0
	}
	mins := int(out.Sub(*in).Minutes()) - lunchMinutes
	if mins < 0 {
		return 0
	}
	return mins
}

// Summary is the monthly timesheet roll-up returned to the UI.
type Summary struct {
	Year             int     `json:"year"`
	Month            int     `json:"month"`
	BusinessDays     int     `json:"businessDays"`
	StandardMinutes  int     `json:"standardMinutes"`
	WorkedMinutes    int     `json:"workedMinutes"`
	LeaveMinutes     int     `json:"leaveMinutes"`     // recognized (연차/공가 등) as worked-equivalent
	OvertimeMinutes  int     `json:"overtimeMinutes"`  // approved overtime
	RecognizedTotal  int     `json:"recognizedTotal"`  // worked + leave
	FulfillmentPct   float64 `json:"fulfillmentPct"`   // recognizedTotal / standard
	DaysPresent      int     `json:"daysPresent"`
}

// Compute assembles the summary from raw minute inputs.
func Compute(year, month, dailyStandardMin, worked, leave, overtime, daysPresent int) Summary {
	std := StandardMinutes(year, time.Month(month), dailyStandardMin)
	recognized := worked + leave
	pct := 0.0
	if std > 0 {
		pct = float64(recognized) / float64(std) * 100
	}
	return Summary{
		Year:            year,
		Month:           month,
		BusinessDays:    MonthBusinessDays(year, time.Month(month)),
		StandardMinutes: std,
		WorkedMinutes:   worked,
		LeaveMinutes:    leave,
		OvertimeMinutes: overtime,
		RecognizedTotal: recognized,
		FulfillmentPct:  pct,
		DaysPresent:     daysPresent,
	}
}